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INTRODUCTION:

There are 2 main types of non-enzymatic browning in food – the Maillard reaction and caramelisation.

The Maillard reaction occurs when reducing sugars and amino acids react with one another, a process that is increased with exposure to heat and gives desirable colour, flavour and aroma to food for example the browning of meat (Appell, M., Hurst, W.J. and Finley, J.W., 2018).

Caramelisation occurs when sugar is exposed to high temperatures for example table sugar to caramel, or the caramel colour and crystallisation of fried banana (Clemens, R.A., Jones, J.M., Kern, M., Lee, S.Y., Mayhew, E.J., Slavin, J.L. and Zivanovic, S., 2016.).

Most of these changes are desirable to the consumer, however in some instances they are not. It is therefore important to be able to investigate and understand the non-enzymatic browning in foods and to what degree a reaction may occur in different fresh food ingredients for use in the food industry and to better preserve foods to maximise both shelf life, consumer satisfaction. By understanding this, the manufacturer may have more control over degree at which non-enzymatic browning occurs and what methods are required to achieve desired effect and to therefore to supply more appealing food product that is visually appealing, flavourful and ideal cooking instruction for uncooked foods (Paravisini, L. and Peterson, D.G., 2018).

MATERIALS & METHODS:

As per lab manual "Food Chemistry – FT4204"

Absorbance @ 40

Reagent Glycine Ascorbic acid H2O pH

1 10mls glucose 5 0 5 4.04 0.001

2 10mls glucose 5 0 5 8.04 0.001

3 10mls glucose 5 5 0 8.00 0.095

4 15mls glucose 0 0 5 8.60 0.000

5 10mls fructose 5 0 5 8.00 0.012

6 10mls sucrose 5 0 5 8.10 0.005

7 10mls sorbitol 5 0 5 7.95 0.001

Absorbance @ 60

Reagent Glycine Ascorbic acid H2O pH

1 10mls glucose 5 0 5 4.04 0.002

2 10mls glucose 5 0 5 8.04 0.069

3 10mls glucose 5 5 0 8.00 0.871

4 15mls glucose 0 0 5 8.60 0.003

5 10mls fructose 5 0 5 8.00 0.220

6 10mls sucrose 5 0 5 8.10 0.005

7 10mls sorbitol 5 0 5 7.95 0.001

DISCUSSION:

 The Maillard reaction occurs when the carbonyl group of a reducing sugar – a sugar that contains an aldehyde or a ketone group (e.g. glucose, fructose), reacts with a free amino group, in this case glycine; to produce N-glycosylamine before then going through the Amadori rearrangement product (ARP). At pH >7 ARP goes through a complex set of reactions as shown in the image below to eventually lead to the production of melanoidins – brown nitrogenous polymer and copolymers.

While the Maillard reaction occurs without heat, it is greatly increased with exposure to heat (Davidek, T. and Davidek, J., 2003).

Figure 1. Maillard reaction scheme adapted from Hodge

Caramelisation occurs when sugar molecules are exposed to high heat, producing a brown colour. It differs from the Maillard reaction in the way that proteins are not involved but instead acid, base or salt presence is necessary. Anhydro rings are formed through the dehydration of the sugar molecule which then condense to form polymers that are brown in colour and contain conjugated double bonds (Wijaya, C.H., Wijaya, W. and Mehta, B.M., 2014).

Image 2 showing caramelisation mechanism.

From the results tables shown above, an increase in temperature from 40C to 60C proved to increase in the reactivity slightly between the glucose and H2O at pH 8.04, moderately for fructose and H20 and significantly in the case of glucose and ascorbic acid. At the lower temperature of 40C fructose showed slight activity but only glucose with the ascorbic acid showed some activity.

You can see from the results that the maillard reaction occurred with the fructose and glycine with the increase in temperature as well as at a much higher rate with glucose, weak acid and glycine. As expected there was no reaction with the disaccharide, sucrose and the amino acid solution, glycine, as it would first have needed to be hydrolysed to fructose and glucose for the Maillard reaction to occur as well as no reaction with the glucose and glycine at the lower pH of 4.04.

Sorbitol is a sugar alcohol formed by the reduction of glucose where the aldehyde group – needed for the reactivity with the free amino, is converted to a hydroxyl group, hence no reaction occurred (Lopez-Galvez, M.I., Lavado, F.M. and Pastor, J.C., 2014).

An example of maillard reaction is the browning of meat when cooked.

No caramelisation occurred as this requires the dehydration of sugar molecules so temperatures would need to be >100C for water to be evaporated off and 110C for the caramelisation of fructose and 160C for sucrose and glucose (Jouppila, K., 2017).

Bread is an example of where both caramelisation and the Maillard reaction occur together.

CONCLUSIONS:

The type of non-enzymatic browning to occurred was Maillard reaction, it is important in food chemistry to be able to effectively control the rate of reaction and to have an understanding of the effect of pH as well as temperature. This is useful in industry in order to use the correct packaging, storage and to correct cooking instructions that will result in greater shelf life, consumer satisfaction and profitability (Van Ba, H., Hwang, I., Jeong, D. and Touseef, A., 2012).

Caramelisation is useful in the food industry for adding a range of caramel flavours and colours to carbonated beverages such as cola, syrups, sweets and in baked goods (Grumezescu, A.M. and Holban, A.M. eds., 2017).

Both are important methods for use in food manufacturing and in the restaurant industry.

REFERENCE:

• Appell, M., Hurst, W.J. and Finley, J.W., 2018. Amino Acids and Proteins. In Principles of Food Chemistry (pp. 117-164). Springer, Cham.

• Clemens, R.A., Jones, J.M., Kern, M., Lee, S.Y., Mayhew, E.J., Slavin, J.L. and Zivanovic, S., 2016. Functionality of sugars in foods and health. Comprehensive Reviews in Food Science and Food Safety, 15(3), pp.433-470.

• Paravisini, L. and Peterson, D.G., 2018. Role of Reactive Carbonyl Species in non-enzymatic browning of apple juice during storage. Food chemistry, 245, pp.1010-1017.

• Davidek, T. and Davidek, J., 2003. 18 Chemistry of the Maillard Reaction in Foods. Chemical and functional properties of food saccharides, p.291.

• Wijaya, C.H., Wijaya, W. and Mehta, B.M., 2014. General properties of major food components. Handbook of food chemistry, pp.1-32.

• Lopez-Galvez, M.I., Lavado, F.M. and Pastor, J.C., 2014. Diabetic Retinopathy: An Overview. In Handbook of Nutrition, Diet and the Eye (pp. 41-51).

• Jouppila, K., 2017. Mono-and disaccharides: Selected physicochemical and functional aspects. In Carbohydrates in Food, Third Edition (pp. 59-114). CRC Press.

• Van Ba, H., Hwang, I., Jeong, D. and Touseef, A., 2012. Principle of meat aroma flavors and future prospect. In Latest research into quality control. InTech.

• Grumezescu, A.M. and Holban, A.M. eds., 2017. Natural and Artificial Flavoring Agents and Food Dyes (Vol. 7). Academic Press.

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